QtWidgets: restore Qt 5 compatibility for save/restore state

Several classes in QWidget use QDataStream internally in order
to save and restore state. These QDataStream usages were not
versioned, meaning that if Qt changes the serialization for some
datatype, then the data saved between different Qt versions becomes
incompatible. Note that the save/restore API in question just produce
opaque blobs as QByteArrays -- the user has no control over the
QDataStream objects and thus versions.

Fix by version the usages.

In QHeaderView this has caused a regression because QBitArray *did*
change version between Qt 5 and 6. In general, using QDataStream without
explicit versioning is a mistake, so deploy the same fix elsewhere as
well.

Fixes: QTBUG-99487
Pick-to: 5.15 6.2 6.3
Change-Id: I82bb5c266f4e5dedc0887cbef855dccab1015e29
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: <doctor.whom@gmail.com>

src/widgets/dialogs/qfiledialog.cpp

@@ -418,6 +418,7 @@ QByteArray QFileDialog::saveState() const
     int version = 4;
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
 
     stream << qint32(QFileDialogMagic);
     stream << qint32(version);
@@ -452,6 +453,7 @@ bool QFileDialog::restoreState(const QByteArray &state)
     Q_D(QFileDialog);
     QByteArray sd = state;
     QDataStream stream(&sd, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     if (stream.atEnd())
         return false;
     QStringList history;

src/widgets/itemviews/qheaderview.cpp

@@ -1742,6 +1742,7 @@ QByteArray QHeaderView::saveState() const
     Q_D(const QHeaderView);
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     stream << QHeaderViewPrivate::VersionMarker;
     stream << 0; // current version is 0
     d->write(stream);
@@ -1763,6 +1764,7 @@ bool QHeaderView::restoreState(const QByteArray &state)
         return false;
     QByteArray data = state;
     QDataStream stream(&data, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     int marker;
     int ver;
     stream >> marker;

src/widgets/widgets/qmainwindow.cpp

@@ -1217,6 +1217,7 @@ QByteArray QMainWindow::saveState(int version) const
 {
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     stream << QMainWindowLayout::VersionMarker;
     stream << version;
     d_func()->layout->saveState(stream);
@@ -1245,6 +1246,7 @@ bool QMainWindow::restoreState(const QByteArray &state, int version)
         return false;
     QByteArray sd = state;
     QDataStream stream(&sd, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     int marker, v;
     stream >> marker;
     stream >> v;

src/widgets/widgets/qmainwindowlayout.cpp

@@ -1164,10 +1164,12 @@ bool QMainWindowLayoutState::restoreState(QDataStream &_stream,
     }
 
     QDataStream ds(copy);
+    ds.setVersion(_stream.version());
     if (!checkFormat(ds))
         return false;
 
     QDataStream stream(copy);
+    stream.setVersion(_stream.version());
 
     while (!stream.atEnd()) {
         uchar marker;

src/widgets/widgets/qsplitter.cpp

@@ -1650,6 +1650,7 @@ QByteArray QSplitter::saveState() const
     int version = 1;
     QByteArray data;
     QDataStream stream(&data, QIODevice::WriteOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
 
     stream << qint32(SplitterMagic);
     stream << qint32(version);
@@ -1691,6 +1692,7 @@ bool QSplitter::restoreState(const QByteArray &state)
     int version = 1;
     QByteArray sd = state;
     QDataStream stream(&sd, QIODevice::ReadOnly);
+    stream.setVersion(QDataStream::Qt_5_0);
     QList<int> list;
     bool b;
     qint32 i;

tests/auto/widgets/itemviews/qheaderview/tst_qheaderview.cpp

@@ -146,6 +146,7 @@ private slots:
     void moveSectionAndReset();
     void moveSectionAndRemove();
     void saveRestore();
+    void QTBUG99487_saveRestoreQt5Compat();
     void restoreToMoreColumns();
     void restoreToMoreColumnsNoMovedColumns();
     void restoreBeforeSetModel();
@@ -1716,16 +1717,24 @@ static QByteArray savedState()
     return h1.saveState();
 }
 
-void tst_QHeaderView::saveRestore()
+// As generated by savedState()
+static const QByteArray qt5SavedSate = QByteArrayLiteral("\x00\x00\x00\xFF\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x01\x00\x00\x00\x02\x01\x00\x00\x00\x04\x00\x00\x00\x02\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x04\x00\x00\x00\x02\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x03\x00\x00\x00\x04\b\x00\x00\x00\x01\x00\x00\x00\x03\x00\x00\x00""d\x00\x00\x00\xD2\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00""d\x00\x00\x00\x00\x00\x00\x00\x84\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00""d\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\n\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00""d\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x03\xE8\x00\x00\x00\x00\x00\x00\x00\x00\x00");
+
+enum class SaveRestoreOption
+{
+    CheckGeneratedState,
+    DoNotCheckGeneratedState,
+};
+
+static void saveRestoreImpl(const QByteArray &state, SaveRestoreOption option)
 {
     QStandardItemModel m(4, 4);
-    const QByteArray s1 = savedState();
 
     QHeaderView h2(Qt::Vertical);
     QSignalSpy spy(&h2, &QHeaderView::sortIndicatorChanged);
 
     h2.setModel(&m);
-    QVERIFY(h2.restoreState(s1));
+    QVERIFY(h2.restoreState(state));
 
     QCOMPARE(spy.count(), 1);
     QCOMPARE(spy.at(0).at(0).toInt(), 2);
@@ -1740,12 +1749,30 @@ void tst_QHeaderView::saveRestore()
     QVERIFY(h2.isSectionHidden(3));
     QCOMPARE(h2.hiddenSectionCount(), 1);
 
-    QByteArray s2 = h2.saveState();
+    switch (option) {
-    QCOMPARE(s1, s2);
+    case SaveRestoreOption::CheckGeneratedState:
+    {
+        QByteArray s2 = h2.saveState();
+        QCOMPARE(state, s2);
+        break;
+    }
+    case SaveRestoreOption::DoNotCheckGeneratedState:
+        break;
+    };
 
     QVERIFY(!h2.restoreState(QByteArrayLiteral("Garbage")));
 }
 
+void tst_QHeaderView::saveRestore()
+{
+    saveRestoreImpl(savedState(), SaveRestoreOption::CheckGeneratedState);
+}
+
+void tst_QHeaderView::QTBUG99487_saveRestoreQt5Compat()
+{
+    saveRestoreImpl(qt5SavedSate, SaveRestoreOption::DoNotCheckGeneratedState);
+}
+
 void tst_QHeaderView::restoreToMoreColumns()
 {
     // Restore state onto a model with more columns